Calorie discrepencies

[Stonewall]

Let me preface this by saying that I know the calorie calculation on ANY piece of fitness equipment is far from perfect. I simply want to understand the math/mechanics of the erg.

I've noticed two inconsistencies with calorie totals:

1. Calorie totals for the same exact time and distance (down to the hundredth) will be different by 1-5 seconds in either direction.
2. This is rare, but the calorie total will be off by several hundred (saying 400 calories burned for a 15K row at sub-2:00 pace).

What causes these two inaccuracies? I appreciate the help!

[Citroen]

Calories on the ergo are a completely made up number if you don't weigh 80Kg, you don't row at 25% efficiency and you don't run 300kCal just to go up and down the slide.

So most rowers ignore them and use pace (time per 500m) to calibrate and compare their workouts. If you need fine grained detail use watts.

[Stonewall]

Calories on the ergo are a completely made up number if you don't weigh 80Kg, you don't row at 25% efficiency and you don't run 300kCal just to go up and down the slide.

So most rowers ignore them and use pace (time per 500m) to calibrate and compare their workouts. If you need fine grained detail use watts.

Yes, I get that, and I don't use calories for training. Again, I'm trying to understand Concept2's math, or figure out if something is simply wrong with my PM.

[JaapvanE]

I've noticed two inconsistencies with calorie totals:

1. Calorie totals for the same exact time and distance (down to the hundredth) will be different by 1-5 seconds in either direction.
2. This is rare, but the calorie total will be off by several hundred (saying 400 calories burned for a 15K row at sub-2:00 pace).

What causes these two inaccuracies? I appreciate the help!

When you look at this description of the underlying physics, you'll notice that power is an essential ingredient of the calorie calculation.

However, there are more ways to end with the same distance/time combo. On the extremes you have (a very energy efficient) steady state and on the other end you have a very energy inefficient negative or positive split. This is due to cube law: to go twice as fast, you'll need 8 times the energy. So having a a very stable pace is efficient, while "losing some time" in one spot and "making it up somewhere else" requires a lot more energy.

So, you get different calorie counts because you didn't use your energy in the same (optimal) way as as your other rowing session.

[Stonewall]

I've noticed two inconsistencies with calorie totals:

1. Calorie totals for the same exact time and distance (down to the hundredth) will be different by 1-5 seconds in either direction.
2. This is rare, but the calorie total will be off by several hundred (saying 400 calories burned for a 15K row at sub-2:00 pace).

What causes these two inaccuracies? I appreciate the help!

When you look at this description of the underlying physics, you'll notice that power is an essential ingredient of the calorie calculation.

However, there are more ways to end with the same distance/time combo. On the extremes you have (a very energy efficient) steady state and on the other end you have a very energy inefficient negative or positive split. This is due to cube law: to go twice as fast, you'll need 8 times the energy. So having a a very stable pace is efficient, while "losing some time" in one spot and "making it up somewhere else" requires a lot more energy.

So, you get different calorie counts because you didn't use your energy in the same (optimal) way as as your other rowing session.

Thank you for the reply.

So uneven pacing affects the calorie calculation? I take it that's why calorie totals for interval workouts with active recovery are so different than what the calculator says it should be for the same total time and distance.

[JaapvanE]

So uneven pacing affects the calorie calculation? I take it that's why calorie totals for interval workouts with active recovery are so different than what the calculator says it should be for the same total time and distance.

Yep, in a nutshell. The PM5 calculates calories for each individual stroke, and uneven pacing or intervals lead to high intensity sections with a disproportionate energy expenditure compensating for low intensity sections wit a tiny bit less energy expenditure. Most calculators assume a steady state pace (the most energy efficient approach).

Please note that intervals are a good training tool. A negative or positive split might be energetically less efficient but might feel more natural to people as they settle in their session. I typically see my split go down a bit as I settle in my rythem.

[gvcormac]

As noted, the same distance at higher speed will consume more calories.

The main problem with the PM calorie calculation is that it gives you 300 cal/hr credit just for being alive. If you subtract 300 cal/hr (5 cal/min) from the number shown, you get a decent approximation of net calories consumed by your exercise.

This morning I BikeErged in 47 minutes and the PM5 claimed 433 Calories. So my net Calorie burn is 433 - 5*47 = 198.

[Ombrax]

For me the simpler thing is to think in terms of work performed (Avg watts x time) and just ignore the calories.

There are so many variables, you could have 20 different rowers do a 30 minute workout, all of which have the exact same avg power, and in reality (ignoring what the PM says) there would be 20 different "reality" calories burned. Just forget about calories and think of energy or work - the PM does a much better job of telling you that.

Caveat - one thing I do find useful is this: assuming the "calories burned" is roughly correct, it gives you idea of how much work you have to do on the erg to burn off the calories you get from say, a single chocolate chip cookie or a doughnut - A LOT! Put in that context, it makes it easier to not have that tempting oatmeal cookie when someone brings a batch in to work.